Blade mounting for rotary lawnmowers



Feb. M, 958 J. E. HAFFEE BLADE MOUNTING FOR ROTARY LAWNMOWRRS FiledMarch s, 195e n n n l l l l n I nite rates This invention relates to newand useful improvements in rotary lawn mowers, and has particularreference to the mounting means for attaching the blade orblade-carrying bar on the power driven shaft.

One important object of the present invention is the provision of `ablade mounting which, although made up and secured by a single screwthreaded axially into the arent power shaft, does not depend on saidscrew to retain the Y blade in centered and balanced relation to theshaft. Instead the blade is centered on a relatively heavy portion ofthe mounting, independently of the screw. In previous mountings whereinthe relatively weak screw itself provided lateral support of the blade,the screw often was bent if the blade struck an obstruction, withresultant unbalance of the blade. Such unbalance of the blade causedviolent and often destructive vibration on continued rotation of theblade.

Another important object of the present invention is the provision of ablade mounting of the class described wherein the blade is permitted torotate in its mounting, or vice versa, if the blade strikes anobstruction or if the drive shaft should turn in a reverse direction ason kickback of a gasoline engine driving the same, without loosening thescrew. In previous mountings such loosening of the screw could occur,with the resultant consequences that the screw could become entirelydisengaged and permit the blade to be thrown outwardly with danger toany bystander. This feature also reduces the possibility that the driveshaft itself will be bent by shocks thereto which occur when a bladestrikes an obstruction.

A still further important object is the provision of a blade mounting of`the character described which is yieldably fracturable or bendable inresponse to certain types of shocks or blows to the blade caused bystriking rocks, stumps, sidewalks, etc., in such a manner as to preventthe bending of the drive shaft. The blades and mounting are relativelyinexpensive and easily replaced, while a bent drive shaft necessitatescostly major repairs.

Other objects are simplicity and economy of construction, eiiiciency anddependability of operation, and adaptability for use with many types andsizes of blades.

With these -objects in view, as well as other objects which will appearin the course of the specification, reference will be had to thedrawing, wherein:

Fig. 1 isa central vertical sectional view through a rotary laWnmOWer,with parts leftrin elevation, showing a blade mounting embodying thepresent invention.

Fig. 2 is an enlarged, foreshortened sectional view taken on line lI-IIof Fig. 1, and

Fig. 3 is an enlarged fragmentary sectional view taken on line III-Illof Fig. 2.

Like reference numerals apply to similar parts throughout the severalviews, and the numeral 2 applies to the frame of a rotary lawnmower,said frame being of inverted dish-shape and being formed of metal orother suitable material. Attached rigidly to the upper side of saidframe, as by adjusting screws 4, is a power unit 6, which may be eitheran electric motor or an internal combustion engine. The drive shaft 8 ofsaid power unit extends vertically downwardly through a hole 10 formedtherefor in said frame, and has a cutter bar or blade 12 attached to thelower end thereof by means of a mounting device embodying the presentinvention and designated generally by the numeral 14. Said bladenormally has the form of an elongated flat bar, secured at its mid-pointin mounting l-i and disposed symmetrically thereto whereby it isdynamically balanced relative to `drive shaft 8. Blade 12 has litsopposite lateral edges sharpened respectively at opposite ends thereof,as indicated at 16, to form cutting edges. engaging wheels, not shown,whereby blade 12 is supported at mowing elevation above the ground, andwith suitable propelling or guiding means, also not shown.

Blade mounting i4 comprises a tubular metal body member 18 adapted totit snugly over the lower end of drive shaft 8 in coaxial relationtherewith. Said body is provided with an internal shoulder 2i) limitingthe insertion of the drive shaft, and is secured against rotation onsaid drive shaft by a key 22. The lower end of drive shaft S is axiallydrilled and tapped as at 24 to receive a screw 25 as will be describedhereinbelow. Body member 18 is provided with an integral peripheral ange26 disposed in spaced relation above the lower end of the, body, thelower face of said flange being disposed accurately at right angles tothe axis of the mounting. Said flange is provided `at its peripheraledge with an upstanding integral lip 28, and body i8, ilange 26 and lip28 are joined by a plurality yof Iangularly spaced radial fins 30extending between said body and said lip and formed integrallytherewith.

The portion of body 18 'extending below flange 26 forms a circular boss32-over which blade 12 is tted, a hole 34 being formed centrally in theblade for this purpose. This hole should t closely but freely over theboss. A planar washer 36 having the same diameter as ilange 26 1ssecured against the lower face of boss 32 by screw 25, the face of saidboss being smooth and unbroken except for the hole 3S formedtherethrough to receive said screw, 1n order to insure a broadmetal-to-metal contact between the boss and the washer. Washer 36 maythus be considered as a flange attached to the body and corresponding toange 26, except that it is disposed below instead of above the blade.Also disposed 4on boss 32 are a pair of compressible rubber washers lildisposed respectively between blade 12 and ilange 26, and between blade12 and washer 36. Said rubber washers are of such `density and thicknessthat they are compressed as washer 36 is drawn up tight against boss 32by screw 25. A second washer 42 is also carried on screw 25, betweenwasher 36 and the head of the screw. It is smaller in diameter thanwasher 36, and may be equal to or slightly larger than the diameter ofboss 32.

The mounting as described is believed clearly to accomplish the objectsfirstly above outlined. Firstly, it is apparent that the blade iscentered and balanced on boss 32 of the relatively large and strong bodymember, `and does not depend in -any way on the relatively small andweak screw 25 for lateral support. Thus the blade is much more stronglysupported against being knocked oil? center relative to the drive shaftif said blade should strike a rock or other obstruction. In previousmountings wherein the blade is centered on the screw, any such lateralblow could comparatively easily bend the screw and thus unbalance theblade, with the result that continued operation would cause a radicaland often destructive vibration.

Secondly, the mounting as shown will permit rotation of the blade in itsmounting without loosening screw 25. Screw 25 has a right-handed thread,and the blade turns in a clockwise direction as viewed from above, sothat Patented Feb. 11, 1958 Mower frame 2 is provided with suitableground-r any normalrresistance to rotation of the blade will tend totighten the screw. Nevertheless, -under certain circumstances, such aswhen a kick-back or reverse rotation occursV in power unit 6, if saidunit isa gasoline engine, or when the blade rebounds in a reversedirection after striking an obstruction, there may be a pronouncedtendency for the blade rotation to be transmitted through washer 36 tothe screw, and to loosen the screw, with the danger that the screw willeventually be disengaged and the blade thrown. 'This will not occur inthe present device since the blade is held only frictionally betweenrubber washers, and will slip therebetween before sutiicient torquestrain is built up to cause washer 36 to turn relative to boss 32, sincethe contact between said washer and boss is metal-to-rnetal and may bevery tight. The proper frictional grip on the blade provided by rubberwashers 40 may be regulated by providing washers of the properyieldability and thickness, although this has not been foundparticularly critical. The mounting can easily be adapted to use withthicker or thinner blades by the substitution therein of thicker orthinner rubber washers. Also, the frictional blade mounting permits theshaft 8 to continue rotation, at least for a short time, in the eventthe movement of the blade is arrested by striking an obstruction. Thishas been found to reduce substantially the possibility that such animpact might cause bending of shaft 8.

Thirdly, it will be seen that if either end of the blade is deflectedforcibly upwardly or downwardly by striking an obstruction, `and thishas been found to be an occurrence commoner by far than the simplestoppage of the blade by a square impact, the upward or downward strainof the blade will be transmitted either to flange 26 of the body member,or to the flange constituted by the rim portion of washer 36. Thestrength of these flanges, relative to shaft 8, is such that they willyield, either by bending or cracking, before shaft 8 is strainedsufficiently to be permanently bent. Continued upward or downwarddeflection of the blade will of course bend the blade, but thetransverse line of bend of the blade will then be located directly atthe periphery of body 18 (or the periphery of washer 42), and not at theperiphery of flange 26 or washer 36. The bending force on the blade willthus have a much smaller moment tending to bend shaft 8, and the shaftwill be protected against damage. it would of course be possible toprotect shaft 8 against damage in these circumstances by using alighter, thinner blade, or by notching or otherwise weakening the blade,but this is objectionable as the blade is then much less rugged and lserviceable. The present construction permits the use of a rugged, heavyblade without endangering the shaft. A square impact of the bladeagainst an obstruction, without upward or downward deflection, mightstill cause bending of the shaft. However, as previously stated, thishas been found to be a relatively rare occurrence and even in such rarecases the likelihood of bending the shaft is materially reduced by thefact that the shaft may continue to turn `due to its frictionalattachment to said blade.

The inventor has heretofore formed body 18 and flange 26, of a light,inexpensive, but relatively Weak metal such as produced by die-castingor the like, in order to render the replacement thereof when damaged asinexpensive as possible. With such metal, it has been found desirable toreinforce flange 26 by webs 30. The yield- `ability and strength of theflange may be regulated by varying the size, number and spacing of thesewebs. However, this is not an essential feature, and if the body and itsflange were formed of steel or other stronger metal as is washer 36,such reinforcement would be unnecessary. The use of additional washer 42prevents the possibility` that if washer 36 were bent downwardly by theblade as described above, it might bend at screw 2S. This could loosenwasher 36 from boss 32, permit ting relative rotation thereof, and mightalso bind or crimp the screw so that it would turn with the washer 36,with consequent danger that the screw might become disengaged from theshaft. Washer 42 confines the bending of Washer 36 to an area outside ofthe contact area between washer 36 and boss 32, and thereby prevents theoccurrence just describe-d. The same result could be accomplished bythickening the central portion of washer 36, but the use of two simpleplanar washers is more economical.

Although I have shown and described a specic embodiment of my invention,it will be readily apparent that numerous changes of structure andoperation could be made without departing from the spirit of theinvention as defined by the scope of the appended claims.

What I claim as new and desire to protect by Letters Patent is:

l. In combination with -a lawnmower including a power driven verticaldrive shaft, a mounting body having a socket formed in the upper endthereof in which the lower end of said drive shaft is engaged, anelongated blade bar having a central aperture formed therethroughthrough which said body extends, a fixed ange carried by said body abovesaid blade bar, a screw extending upwardly through said body andthreaded into said drive shaft, a detachable ilange constituting aplanar washer secured against the lower end of said body by said screw,said washer being held in non-rotating relation to said body by reasonof metal-to-metal contact therebetween, and a pair of friction washersdisposed respectively between said blade bar and said fixed flange andbetween said blade bar and said detachable ange, said anges pressingsaid friction washers against said blade bar whereby rotation of saidblade bar relative to said body is yieldably resisted.

2. The structure as recited in claim 1 with the addition of meansreinforcing the central portion of said detachable flange washer againstbending, and wherein the edge portion of said washer and said xed flangeare suiciently thin in a direction parallel to the axis of the driveshaft to possess substantially less bending strength than said driveshaft, whereby upward or downward force on either extended end portionof said blade bar will cause bending of one or the other of saidflanges, rather than bending of said drive shaft.

References Cited in the file of this patent UNITED STATES PATENTS2,651,530 Blydenburgh Sept. 8, 1953 2,707,362 Thelander May 3, 19552,721,438 OMalley Oct. 25, 1955

